[Paraview] [ParaView] Off axis Projection and Stereo

Wed Nov 30 03:37:06 EST 2011

Hello Aashish,

thanks for your valuable answers. I'm glad to know that these problems being
addressed in vtk development. And yes, I have some more questions. :-)

Please, can you explain, why EyeAngle is ignored during Off-Axis ? Is there
an idea behind this approach? I know the formulation from the paper to
construct the view matrix. And I know, only the eye points (not their
directions) are considered. 

BTW: Why is the viewing direction ignored, during Off-Axis-Calculation?

I'm really looking forward to read your answers :).

Thank you very much.

Cheers,
Stephan

-----Ursprüngliche Nachricht-----
Von: Aashish Chaudhary [mailto:aashish.chaudhary at kitware.com] 
Gesendet: Mittwoch, 30. November 2011 00:22
An: Stephan Rogge
Cc: paraview at paraview.org
Betreff: Re: [Paraview] [ParaView] Off axis Projection and Stereo

Hi Stephen.

On Thu, Nov 24, 2011 at 5:34 AM, Stephan Rogge <Stephan.Rogge at tu-cottbus.de>
wrote:
> Hello,
>
> Since I can use ParaView's cave mode in my Virtual Environment (VE), I 
> was able to play a bit with its stereo capabilities and the wall 
> configuration (.pvx).
>
> Before I start with my discussion, I would like to give some details 
> off my
> configuration:
>
> * Virtual Environment
>     - two back projected walls (passive stereo)
>     - each wall is 2.6 m width  x 1.6 m high
>     - the walls creates an arrow with an angle of 112°
>     - a render PC with two NVIDIA QUADRO 5000 (one GPU per wall) is 
> connected to four projectors
> * ParaView
>    - To obtain a correct un-distorted image we use the edge points 
> (world
> coordinates) of the walls to configure the two views in the pvx-file
>    - Since we use Windows 7, I was not able to define the GPU - View 
> assignment in the pvx-file
>       (it seems to be, that under Windows the flag 
> 'Environment="DISPLAY=:0"' is being ignored, all views presented on 
> the first display). We had to
>       modify "vtkPVSynchronizedRenderWindows", to align the views in 
> respect to the MPI process id.
>    - Further code modification has been done to control the stereo 
> parameters EyeSeparation and EyeAngle
>
> #############################
> ## Multiple Display Support (Win7) ##
> #############################
>
> And here I like to start my discussion. At first let's talk about the 
> display configuration. I had to modify 
> "vtkPVSynchronizedRenderWindows" to use my two walls under Windows 7. 
> I can imaging, that this is not the best solution. May be some 
> problems can appear here? Please, can some of the developer comment 
> this code modification? This is the code snippet:
>
> void vtkPVSynchronizedRenderWindows::UpdateWindowLayout()
> {
>      .....
>      else if (in_cave_mode)
>        {
>        if (vtksys::SystemTools::GetEnv("PV_ICET_WINDOW_BORDERS"))
>          {
>          this->Internals->SharedRenderWindow->SetSize(400, 400);
>          }
>        else
>          {
>          this->Internals->SharedRenderWindow->SetFullScreen(1);
>
>          // These two lines here has been added
>          unsigned int id =
> vtkMultiProcessController::GetGlobalController()->GetLocalProcessId();
>          this->Internals->SharedRenderWindow->SetPosition(1920 * (id), 
> 0);
>         }
>      }
>      .....
> }
>
> ###########################
> ## Stereo Control in Cave Mode ##
> ###########################
>
> When I visualize a small object in my ParaView Cave setup, I realized 
> that the parallax between left and right image became un-natural big (it
hurts).
> My opinion is, when we change the zoom we need to adjust the eye 
> separation (and / or the eye angle). This can be done manually or 
> automatically to yield the optimal stereoscopic impression.
> An parallel project from Aashish Chaudhary (on gitorious), address 
> this problem and starts to modify the VTK api, to have some control of
stereo.
> Unfortunately, after reading some parts of this source code, it looks 
> like only EyeAngle can be manipulated. Furthermore  changes of that 
> parameter were not considered during OffAxisProjection calculation. 
> The algorithm considers only the 3D points of left and right eye and 
> not their angles. Thus, changes of eyes angle does not have an effect 
> on images displayed in my cave.
> I've noticed a code part were the eye angles for left and right were 
> only applied, when UseOffAxisProjection is turned off. And this is not 
> the case when I use ParaView with my view settings. Would it be wrong, 
> if we modify the IF-condition in 
> vtkCamera::ComputeProjectionTransform() in order to consider always the
angle:
>
> if ( this->Stereo /*** &&!this->UseOffAxisProjection ***/)   // <----- 
> Disabling the check for Off-Axis-Calculation
>    {
>    // set up a shear for stereo views
>    if ( this->LeftEye )
>      {
>      this->ProjectionTransform->Stereo( -this->EyeAngle/2,
>                                          this->Distance ); .....

Sorry it took me some time to reply. Basically in VTK there could be
various ways to get the stereo. With in Crystal eyes stereo we have
two options now,

1. Legacy stereo
2. Off axis stereo

Second is the one added recently. In VTK camera now if you set
SetUseOffAxisStereo(1) it uses 2) for stereo calculations and hence
EyeAngle in that case is ignored.

Look at the test code here:
VTK_SRC_DIR/Rendering/Testing/Cxx/TestOffAxisStereo.cxx

You can control eye separation if you choose 2).  I have added notes
on the code about this but I will make it even more explicit.

>
> Another problem arises, when I want to adjust the eye separation. I had to
> modify a couple of VTK source code files to provide the eye separation as
an
>
> proxy property and to distribute it along all mpi processes. Is it planned
> to provide this parameter globally?

We are going to work on this again very soon. We can take care of this
there then. Well the idea is that we will have a more descriptive
config file ( + UI in ParaView client) where you could specify eye
separation as well.

>
> Please, let me know, what you are thinking about my ideas.

Let me know if you have some more questions. One thing I must add is
we ran into some clipping issues in ParaView and we are hoping to
address that soon. Related to this we have paraview code out there
which is not checked in master yet.

>
> Best regards
> Stephan
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the ParaView Wiki at:
http://paraview.org/Wiki/ParaView
>
> Follow this link to subscribe/unsubscribe:
> http://www.paraview.org/mailman/listinfo/paraview

-- 
| Aashish Chaudhary
| R&D Engineer
| Kitware Inc.
| www.kitware.com